For centuries, it has been known that the surface of a liquid in gravitational fields can have a high optical quality shape. In order for this to be the case, the surface must be free of surface excitations which can result from vibration and air motion.
More recently, Wood recognized the possibility of creating parabolic mirrors by rotating liquids in a gravitational field (see Wood, R. W. 1909, ApJ, 29, 164). After the liquid has achieved a uniform angular velocity, in the absence of wind, its surface in a uniform gravitational field is a perfect paraboloid. Wood showed that if the liquid is mercury, it is in principle possible to produce mirrors of optical quality at low cost. The problems that Wood encountered in such devices, namely waves and ripples in the mercury surface resulting from inadequate rotational speed control and vibrations introduced by the rotor bearing, have been addressed by Borra and his collaborators (see Borra, E. F., 1983, JPASC, 76, 245; Borra et al, 1989, ApJ, 346, L41; Borra et al, 1992, ApJ, 389, 829; and, Borra et al, 1993, ApJ, 418, 943). Basically, Borra et al used higher quality bearings and high quality drive mechanisms to eliminate such vibrations. Further improvements were obtained by using a very thin layer of mercury in order to increase damping of any surface ripples.
Although mirrors formed by fluid surfaces in gravitational fields are seen to have many potential uses because of their low cost, they do have one major restriction--namely that they must be predominately horizontal. In other words, a vector perpendicular to the center of the mirror must be vertical, regardless of whether the mirror is flat or curved by rotational affects. The present invention addresses this deficiency.